Chlorinated aliphatic hydrocarbons have long been used as degreasing agents to clean metal parts in the course of manufacturing, maintenance and repair of machinery. These agents have also been in wide use for many years as dry cleaning agents or as solvents in the chemical and related industries. More recently, these agents have been extensively used in the electronics industry. In the long history of these agents, they were frequently disposed of in an indiscriminate manner, or as leakage from holding tanks. This has resulted in chlorinated aliphatic hydrocarbons becoming a major contaminant of groundwater. Among chlorinated aliphatic hydrocarbons, 1,1',2-trichlorethylene (TCE) is the most prevalent environmental contaminant and is found in more National Priority Landfill sites than any other single chemical.
Since chlorinated aliphatic hydrocarbons are toxic and often convertible into even more toxic compounds (for example, tetrachloroethylene is converted into vinyl chloride, a human carcinogen, under anaerobic conditions by bacteria), it is important to find ways to remove them from groundwater, which is the source of drinking water for much of the population. Currently, the most commonly utilized technology for removal of TCE from groundwater is "air stripping", followed in frequency of use by activated carbon absorption. Both of these methods merely move the TCE from one compartment to another, with dilution (in the air) during air stripping or concentration on the carbon by absorption in the latter case. Further, air stripping may soon be outlawed in some parts of the country and carbon absorption creates solid, toxic waste.
Certain bacteria have been reported to degrade TCE, including some anaerobic methanogens (methane-forming bacteria), some aerobic bacteria that degrade one-carbon compounds by preference (methanotrophs), and some toluene-degrading aerobic bacteria. See Brouwer et al., Appl. Environ. Microbiol., 45, 1286 (1983); Vogel et al., Appl. Environ. Microbiol., 49, 1080 (1985); Little et al., Appl. Environ. Microbiol., 54, 951 (1988); Wilson et al., Appl. Environ. Microbiol., 49, 242 (1985); and Nelson et al., Appl. Environ. Microbiol., 54, 604 (1988), respectively. The methanogens are, however, very hard to work with since they are strict anaerobes that have relatively slow specific rates of TCE destruction (with the possibility of forming vinyl chloride from chlorinated aliphatic hydrocarbon congeners found together with TCE) See Vogel et al , supra. The methanotrophs have a more rapid rate of TCE conversion than methanogens, but the time course of their attack upon TCE suggests that TCE is in some way toxic to the cells or to the enzyme(s) functional in TCE conversion. See Wackett et al., Appl. Environ. Microbiol., 54, 1703-1708 (1988). This set of observations is also true of some aerobic bacteria that degrade toluene. See Wackett et al., supra.
In many cases TCE is a co-contaminant with various hydrocarbon fuels, such as gasoline. Accordingly, there is a need for a method to isolate aerobic bacteria that are capable of rapid degradation of TCE while concomitantly metabolizing other hydrocarbon compounds as sources of carbon and energy for growth.